Remove unused FrameGeneratorCapturer::Create signature

Bug: webrtc:7671
Change-Id: I4102d963d5d6867d35172b97c5b3ffff1f00231a
Reviewed-on: https://webrtc-review.googlesource.com/61342
Commit-Queue: Emircan Uysaler <emircan@webrtc.org>
Reviewed-by: Niklas Enbom <niklas.enbom@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22393}
diff --git a/test/frame_generator.h b/test/frame_generator.h
index d12072a..5728cfa 100644
--- a/test/frame_generator.h
+++ b/test/frame_generator.h
@@ -59,8 +59,11 @@
   }
 
   enum class OutputType { I420, I420A };
+
   // Creates a frame generator that produces frames with small squares that
   // move randomly towards the lower right corner.
+  // |type| has the default value OutputType::I420. |num_squares| has the
+  // default value 10.
   static std::unique_ptr<FrameGenerator> CreateSquareGenerator(
       int width,
       int height,